Abstract
This study reports a novel non-label detection of UV-absorbing proteins by thermal lens microscopy (TLM) using a visible excitation. The detection is enabled by utilizing the optical near-field (ONF) generated on nanostructures. Owning to its apparent high energy, here the ONF allows the optical excitation of molecules, even though the energy of incident photon is lower than the absorption energy of molecules. As a result, the detection of zeptomole of UV-absorbing proteins in a detection volume of ∼20aL has been realized. Our method is conceptually novel in overcoming the lack of appropriate excitation laser sources for detection of biomolecules such as proteins, DNA, etc., which usually have optical absorption in the UV range. It also promises important implications in detection for bioanalysis in ultra-small (∼101 nm) spaces.